In magnetic disk devices such as hard disk drives (HDDs), a contact start and stop (CSS) system is employed in which a magnetic head is brought into contact with a contact slide area (CSS area) located in the inner-circumferential area of the magnetic disk surface when stopped, and the magnetic head flies upward while sliding in contact with the disk surface in the CSS area and then recording or reproduction is conducted in a disk area surface for recording and reproduction that is located to the outside of the CSS area when activated. When an operation has been completed, the magnetic head is withdrawn from the recording and reproduction area into the CSS area, after which the magnetic head descends while sliding in contact with the disk surface in the CSS area and comes to a stop. In the CSS system, the operations of starting and terminating in which sliding contact occurs are called CSS operations.
In a magnetic disk employing the CSS system, it is necessary to provide both a CSS area and a recording and reproduction area on the disk surface. It is also necessary to provide an uneven topography having a certain surface roughness on the magnetic disk surface so that the magnetic head and magnetic disk do not adhere to each other when in contact.
To reduce the damage caused by the magnetic head sliding in contact with the magnetic disk during CSS operations, a magnetic recording medium in which a coating of a perfluoroalkylpolyether lubricant of the structure HOCH2—CF2O—(C2F4O)p—(CF2O)q—CH2OH is applied is known, for example, through Japanese Unexamined Patent Publication (KOKAI) Showa No. 62-66417 (Patent Reference 1).
Similarly, magnetic recording media of high CSS durability are known through Japanese Unexamined Patent Publications (KOKAI) Heisei No. 9-282642 (Patent Reference 2) and Heisei No. 10-143838 (Patent Reference 3).
Recently, magnetic disk devices based on the load-unload (LUL) system have been introduced as substitutes for the CSS system. In the LUL system, the magnetic head is withdrawn to an inclined base, called a “ramp”, positioned beyond the disk when stopped. When activated, the magnetic disk is caused to rotate, after which the magnetic head slides over the magnetic disk from the ramp to conduct recording and reproduction. This series of operations is referred to as LUL operations. Since a broader recording and reproduction area can be ensured on the magnetic disk surface than in the CSS system, the LUL system is desirable for achieving high information capacity. Further, since the uneven topography employed in the CSS system is not required on the magnetic disk surface, the magnetic disk surface can be made extremely smooth. This permits a significant decrease in the flying height level of the magnetic head, making it possible to achieve high S/N ratios for recording signals.
With the introduction of the LUL system, as the magnetic head flying height level has decreased sharply in discontinuous fashion, the requirement that a magnetic disk stably operate even at an extremely low flying height level of 10 nm or less has emerged. However, when the magnetic head is moved rapidly while flying over the surface of the magnetic disk at an extremely low level, there are problems in that “fly-sticking” impairment and head corrosion impairment frequently occur.
“Fly-sticking” impairment refers to impairment in the form of modulation in the position and flying level of the magnetic head during flying. It is accompanied by irregular reproduction output. In some cases, the magnetic disk contacts the magnetic head during flying, causing the head to crash and damaging the magnetic disk.
“Corrosion” impairment refers to impairment in the form of the corrosion of elements of the magnetic head that creates problems during recording and reproduction, and in some causes, renders recording and reproduction impossible. The corroded elements sometimes expand, damaging the surface of the magnetic disk during flying.
Recently, the rotational speed of the magnetic disk has been increased to enhance the response time of the magnetic disk device. The rotational speed of 2.5-inch magnetic disk devices of small diameter suited to mobile applications was formerly 4,200 rpm, but has recently been increased to 5,400 rpm and above to enhance response characteristics.
When the magnetic disk is rotated at such high speeds, a phenomenon occurs in which the centrifugal force accompanying movement causes the lubricating layer to migrate, resulting in nonuniformity of the thickness of the lubricating layer within the magnetic disk surface.
When the thickness of the lubricating layer is increased on the outer circumference portion of the disk, fly-sticking impairment and head crashing impairment tend to occur when the magnetic head enters from the outer circumferential portion of the disk during an LUL operation. When the thickness of the lubricating layer is reduced on the inner circumferential portion, the reduction in lubricating performance tends to cause head crashing.
The lubricating techniques described in above-cited Patent References 1, 2, and 3 that have been employed thus far were primarily developed with emphasis on improving CSS operations. When they are employed in LUL-system magnetic disks, the frequency of the above-described impairments is high, and it is already difficult to satisfy the reliability that has recently come to be required of magnetic disks. Thus, they have become factors impeding the development of high-capacity, high S/N ratio, rapid-response LUL-system magnetic disks.
Based on such problems, the present invention has for its object to provide a magnetic disk, particularly a load-unload magnetic disk, equipped with a highly adhesive lubricating layer that is capable of preventing migration even at high rotational speeds of 5,400 rpms and above and that is capable of preventing fly-sticking and corrosion impairment even at extremely low flying levels of 10 nm or less, for example.